Non-native fish control in Colorado River tributaries in Grand Canyon National Park

Authors: Brian D. Healy, Clay Nelson, Emily Omana Smith, Melissa Trammell

Year: 2013 (xlv)

Abstract

The construction of Glen Canyon Dam resulted in profound changes to the historically warm and turbid waters of the Colorado River within Grand Canyon National Park (GCNP). Non-native salmonids initially stocked in tributaries in the 1920’s and 30’s, proliferated following dam construction. Grand Canyon’s native warmwater fishes, including endangered humpback chub and razorback sucker, continue to be threatened by non-native fishes and habitat alterations. To meet National Park Service (NPS) management goals for native species and to meet the intent of non-native fish control conservation measures included in various U.S. Fish and Wildlife Biological Opinions for the operation of Glen Canyon Dam, GCNP, in cooperation with the Bureau of Reclamation and others, is implementing non-native fish control efforts in Colorado River tributaries. The objectives of these efforts is to improve survival of translocated humpback chub, to minimize predation upon humpback chub and other natives species in both tributaries and the Colorado River, and to restore native fish communities to the extent possible. Mechanical removal methods are the primary focus of control efforts, and abundance and survival estimates calculated using mark-recapture and depletion analysis methodology are used to evaluate the projects, including the evaluation of potential harmful effects of sampling gear upon native species. Preliminary results indicate that changes in size structure and abundance of non-native trout have occurred following removal efforts, as well as improvement of humpback chub survival. Negative effects of control methods (electro-fishing) upon native fish survival were not apparent. Analysis of data collected during a stream-wide (approximately 13 miles) multiple-pass backpack electro-fishing removal effort is ongoing.